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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  112 


BY   S.  A.  FORBES 
STATE  ENTOMOLOGIST 


URBANA,  JANUARY,   1907 


SUMMARY  OF  BULLETIN  No.  112. 


1.  History  of  the  cottony  maple  scale  in  Illinois,  and  especially  recent 
history  in  and  about  Chicago.  Page  343. 

2.  Injurious  effects  of  infestation  of  trees.  Page  345. 

3.  Trees  most  likely  to  be  injured  are  the  soft  maple,  box-elder,  and  the 
basswood.     Other  trees  and  shrubs  liable  to  injury.  Page  346. 

4.  L/ife  history  of  the  insect.    Single  brooded.    Males  perish  before  win- 
ter; females  survive,  partly  grown,  on  twigs  and  smaller  branches.     Page  347. 

5.  The  hatching  period  is  from  June  15  to  July  20;  the  beginning  varies 
as  much  as  two  weeks,  according  to  latitude  and  weather.  Page  349. 

6.  Summer  experiments  with  kerosene  emulsion.     One   application   of 
10  per  cent,  emulsion,  at  middle  of  hatching  period,  killed  about  two  thirds  of 
the  scales,  and  two  applications,  at  middle  and  end  of  hatching  period,  killed 
about  four  fifths.  Page  349. 

7.  Winter  insecticide  measures  more  effective,  a  single  treatment  with 
19  or  20  per  cent,  emulsion  killing  from  86  to  91  per  cent,  of  the  insects. 

Page  353. 

8.  Diseased  or  weakened  trees  liable  to  serious  injury  by  the  kerosene 
sprays.  Page  355. 

9.  Protection  of  roots  against  excess  of  insecticide  suggested. 

Page  356. 

10.  Successful  use  in  Colorado  of  a  winter  spray  containing  only  one 
sixth  of  kerosene.  Page  356. 

11.  Insect  enemies  of  the  scale  which  have  been  found  most  effective  for 
its  destruction.  Page  357. 

12.  Summary  and  general  discussion.  Page  358. 


PLATE  1.     SOFT  MAPLE  TREE  SPRAYED  WITH  20  PER  CENT.  KEROSENE  EMULSION 

JANUARY  19,  AND  PHOTOGRAPHED  JUNE  23,  1906. 

ORIGINALLY  A  SOUND  TREE. 


THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS. 

The  cottony  maple  scale*  is  a  native  insect  parasite  of  the  soft 
maplef ,  rarely  if  ever  injurious  to  the  scattering-  trees  of  this  species 
growing  in  natural  forests,  but  so  destructive  to  them,  and  to  other 
ornamental  trees  as  well,  where  these  are  grown  in  rows  or  groups 
along  streets  or  in  parks  and  on  private  lawns,  that  its  control  has 
become  an  object  of  primary  importance  to  all  owners  and  lovers  of 
some  of  our  most  beautiful  and  popular  American  trees.  In  and 
about  Chicago  especially,  it  has  destroyed,  within  the  past  five  years, 
thousands  of  trees,  beautiful  and  valuable  in  themselves,  and  still 
more  highly  valued  because  of  the  associations  attached  to  them.  To 
do  our  best  to  save  these  noble  but  helpless  products  of  nature  from 
a  slow  and  unsightly  death  by  parasitic  disease,  must  be  the  welcome 
duty  of  all  who  appreciate  the  significance  of  trees  in  the  life  of 
the  people,  and  especially  of  those  who  live  in  our  larger  cities. 

The  history  of  this  insect  in  Illinois  since  1867  exhibits  succes- 
sive periods  of  abundance  and  of  scarcity,  each  averaging  about  four 
or  five  years  for  the  state  as  a  whole.  That  is,  throughout  some 
considerable  part  of  the  state,  and  often  over  most  of  it,  the  maple 
scale  has  been  injuriously  abundant  once  in  eight  or  ten  years,  and 
its  period  of  abundance  has  lasted,  as  a  rule,  about  half  this  time.  In 
any  given  locality,  however,  it  has  usually  been  injurious  for  a  much 
shorter  time,  often  for  not  more  than  one  or  two  years.  The  cessa- 
tion of  its  injuries  and  its  virtual  disappearance  from  the  trees  in- 
fested by  it  have  seemingly  been  clue  almost  wholly  to  the  agency 
of  its  insect  enemies.  . 

An  exception  to  these  statements  is  presented  by  the  existing 
outbreak  of  this  insect  in  northeastern  Illinois,  and  especially  in 
Chicago  and  its  suburbs  to  the  north  and  west.  Here,  as  shown  by 
observations  of  assistants  of  the  office  who  have  been  repeatedly  sent 
through  the  park  and  boulevard  systems  of  Chicago  for  an  investi- 
gation of  insect  injuries  to  shade  trees  and  other  ornamental  vegeta- 
tion, it  has  certainly  been  destructively  numerous  since  1901. 
Indeed,  according  to  information  locally  given  to  Mr.  H.  E.  Weed, 
of  Chicago,  it  has  been  continuously  injurious  over  some  parts  of 
this  area  since  1886.  This  general  persistence  of  an  injurious  in- 
festation within  the  same  district  for  so  long  a  period  is  due  to  the 

*Puh'iHaria  iniiinncrabilix.         ^ Acer  saccharinum. 

343 


344 


BULLETIN  No.  112. 


[January, 


FIG.  t.    A  Soft  Maple  Twig-  badly  infested  with  adults  of  the  Cottony  Maple  Scale. 
About  natural  size.    (J.  B.  Smith.) 


1907.]  THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS.  345 

failure  of  the  insect  enemies  of  this  scale  to  multiply  at  a  sufficient 
rate  to  check  its  rapid  increase,  and  this  is  possibly  the  consequence 
of  an  unfavorable  effect  of  a  city  environment,  although  there  is 
some  reason  to  suppose  that  the  cottony  maple  scale  has  here  ex- 
tended northward  into  a  latitude  more  favorable  to  itself  than  to  the 
insect  enemies  which  commonly  hold  it  in  check. 

Although  no  attempt  has  been  made  to  define  the  present  area  of 
destructive  infestation  in  Illinois,  this  scale  was  reported  to  me  dur- 
ing 1905,  in  the  current  correspondence  of  the  office,  as  locally 
abundant  in  fifteen  counties,  namely,  Winnebago,  Lake,  McHenry, 
Cook,  Dupage,  Kane,  DeKalb,  Ogle,  Bureau,  and  Henry  in  northern 
Illinois;  Woodford,  DeWitt,  Sangamon,  and  Montgomery  in  cen- 
tral Illinois ;  and  Marion  in  the  southern  part  of  the  state.  Doubt- 
less the  actual  area  infested  by  it  was  much  more  general  than  this 
list  would  indicate. 

The  injurious  effect  of  a  severe  and  long-continued  drain  by  the 
cottony  maple  scale  on  the  vitality  of  trees  infested  by  it  is  unques- 
tionable. Many  thousands-  of  soft  maple,  linden,  box-elder,  and  elm 
trees  in  northeastern  Illinois  are  now  dead  or  dying,  or  have  been 
disfigured  by  the  death  of  large  branches,  because  of  injuries  by 
this  insect,  and  large  numbers  of  such  trees  have  been  removed.  Pri- 
vate citizens,  town  boards,  and  park  commissioners  have  become 
deeply  concerned,  and  numerous  inquiries  and  appeals  for  aid  have 
come  to  this  office  during  the  past  three  years.  A  lack  of  available 
funds  has,  however,  prevented  as  active  a  participation  in  the  work 
of  practical  experiment  and  insecticide  operation  as  might  reason- 
ably have  been  expected  of  the  Entomologist's  office,  and  I  have 
been  obliged  to  content  myself,  in  the  main,  with  improving  the 
opportunity  to  observe,  and  incidentally  to  assist,  the  work  of  official 
bodies  and  private  parties  for  the  control  of  this  pest. 

I  am  particularly  indebted  to  Mr.  Reuben  H.  Warder,  Superin- 
tendent of  Lincoln  Park,  who  has  kept  me  acquainted  with  his  work 
against  this  and  other  scale  insects,  and  has  made  it  possible  for  us 
to  follow  his  operations  in  detail  to  their  final  results.  I  am  also 
under  obligations  to  Mr.  O.  C.  Simonds,  Superintendent  of  Grace- 
land  Cemetery,  for  similar  privileges.  Our  field  observations  have 
been  mainly  made  by  Dr.  J.  W.  Folsom,  Associate  in  Entomology 
at  the  University  of  Illinois,  and  by  Mr.  E.  O.  G.  Kelly  and  Mr. 
C.  A.  Hart,  serving  as  assistants  to  the  State  Entomologist.  Dr. 
Folsom  also  managed  a  small  spraying  experiment  for  me  at  Grace- 
land  Cemetery  in  1905. 

The  present  article,  in  the  preparation  of  which  I  have  had  the 
valued  assistance  of  Mr.  Hart,  is  intended  to  give  a  brief  account  of 


346  BULLETIN  No.  112.  [January, 

the  insect,  to  review  the  attempts  made  to  destroy  it  by  means  of 
summer  and  winter  sprays,  and  to  present  practical  instructions 
for  its  mastery  where  it  is  still  present  in  destructive  or  threatening 
numbers. 

A  comprehensive  article  on  the  insect,  prepared  by  Dr.  L.  O. 
Howard,  appeared  in  1900  in  Bull.  22  of  the  U.  S.  Bureau  of  En- 
tomology, and  Circular  64  of  that  Bureau  gives  a  brief  popular 
account  of  it  and  of  measures  to  be  taken  for  its  destruction.  This 
paper  was  prepared  with  special  reference  to  the  Chicago  situation 
of  1905.  In  Bull.  52  of  the  Bureau,  published  in  1905,  is  a  paper 
by  Mr.  H.  E.  Weed  describing  his  experiences  in  spraying  against 
this  scale  in  Chicago,  and  Mr.  S.  A.  Johnson  has  reported  on  some 
experiments  in  Denver,  Col.,  with  a  winter  insecticidal  treatment. 
The  last-mentioned  author  has  this  year  made  the  species  the  subject 
of  Bull.  116  of  the  Colorado  Agricultural  Experiment  Station,  in 
which  a  summer  treatment  is  especially  discussed. 

FOOD  PLANTS. 

The  soft  maple  (Acer  saccharinum}  is  the  tree  most  generally 
and  heavily  infested  by  this  insect.  The  hard  maples,  on  the  other 
hand,  are  infested  but  slightly  if  at  all.  The  box-elder  is  also  greatly 
subject  to  injury,  and  next  to  this,  perhaps,  the  linden  or  basswood. 
Among  the  other  trees  and  woody  plants  often  more  or  less  injured, 
are  the  elm,  honey-locust,  black  locust,  black  walnut,  sumac,  willow, 
poplar,  beech,  hawthorn,  bittersweet,  grape-vine,  and  Viriginia 
creeper.  Dr.  Folsom  found  mature  egg-laying  females  on  the  horse- 
chestnut,  honeysuckle,  dogwood,  trumpet-creeper,  mulberry,  snow- 
berry,  smoke-tree,  Spiraea,  false  syringa  (Philadelfchus'),  and  Wis- 
taria. Oak,  ash,  and  catalpa  are  not  infested  in  northern  Illinois, 
but  injury  to  oak  is  reported  from  Georgia.  According  to  S.  A. 
Johnson,  the  pear  is  most  liable  to  injury  among  the  fruit-trees,  and 
apple,  plum,  and  peach  are  sometimes  infested.  Serious  damage  to 
fruit-trees  is,  however,  very  unlikely.  The  migrating  young,  which 
are  often  washed  from  trees  by  rain,  or  blown  off  in  considerable 
numbers,  may  maintain  themselves  for  a  time  on  a  great  variety  of 
woody  and  herbaceous  plants,  those  on  the  latter,  of  course,  per- 
ishing with  the  advent  of  frosts. 


1907.} 


THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS. 


347 


THE  LIFE  HISTORY  OF  THE  INSECT. 

In  early  summer  this 
scale,  when  very  abund- 
ant, coats  the  under 
side  of  heavily  infested 
limbs  with  a  thick 
layer  of  cotton-like 
waxy  masses  (Fig.  i, 
2),  each  projecting 
from  beneath  a  brown 
cap  or  scale — the  flat 
body  of  the  mature  fe- 
male. This  "cotton"  is 
secreted  and  the  eggs 
are  deposited  within  it 
in  late  May  or  early 
June  in  the  latitude  of 
central  Illinois,  but  usu- 
ally one  or  two  weeks  later  in  the  Chicago  district. 

Something  over  3000  eggs  are  usually  laid  by  each  female,  the 
number  ranging,  in  our  counts,  from  2856  to  3863,  with  an  aver- 


FIG.  2.  The  Cottony  Maple  Scale,  adult  females 
on  twigs.  Natural  size.  (Howard,  U.  S.  Department  of 
Agriculture.) 


•••  ^^ 

FIG.  3.  The  Cottony  Maple  Scale,  immature  stag-es:  a,  newly  hatched  young1,  underside; 
6,  c,  young  female,  top  and  side  views;  d,  young  male;  e,f,  young  on  leaf  and  leaf-stem.  Natu- 
ral size  shown  in  e.  (Howard,  U.  S.  Department  of  Agriculture.) 


age  of  3410.  These  eggs  ordinarily  hatch  in  June  in  central  Illi- 
nois, in  early  July  in  the  northeastern  part  of  the  state,  or  later  if 
the  weather  of  the  time  is  unfavorable.  Virtually  all  are  hatched, 
as  a  rule,  by  the  end  of  July.  The  young  insects  may  crawl  out  on  the 
leaves  and  establish  themselves  beside  the  principal  veins  on  both 


348 


BULLETIN  No.  112. 


[January, 


surfaces  of  the  leaf,  but  most  abundantly  beneath,  or  else  may  locate 
upon  the  twigs.  At  this  season  (Fig.  3)  they  present  the  appear- 
ance of  small,  inconspicuous,  waxy,  elongate-oval  scales,  applied 
closely  to  the  leaf.  They  are  usually  motionless,  but  have  never- 
theless minute 
legs  still  capable 
of  service,  but  in- 
visible unless  the 
insect  is  turned 
over.  Inserting 
their  tiny  beaks 
into  the  tissue  of 
the  leaf,  they  suck 
out  the  sap,  and 
when  the  supply 
of  food  is  large 
they  give  off  the 
excess  in  the  form 
of  a  sticky  fluid, 
the  so-called 
"honey  dew,' 
which  moistens 
the  surface  of  the 


<l 


FIG.  4.  Male  of  Cottony  Maple  Scale:  a,  adult;  b,  c.  an  an- 
tenna and  leg-  enlarg-ed;  d,  e,  second  stage  of  pupa  and  its  cast 
skin;  f.  g,  true  pupa  and  its  cast  skin.  All  greatly  enlarg-ed. 
(Howard,  U.  S.  Department  of  Agriculture.) 


lower   leaves   and 


FIG.  5.  The  Cottony 
Maple  Scale:  adult  fe- 
male in  spring-,  just 
before  I  the  formation 
of  the  cottony  ejrg'-sac. 
(Howard,  U.  S.  De- 
partment of  Agricul- 
ture.) 


falls  on  the  plants  beneath  the  tree.  Under  this 
large  and  constant  withdrawal  of  sap  the  leaves 
turn  pale  or  yellowish,  and  may  fall  off  prema- 
turely, with  the  effect  sometimes  to  kill  the  larger 
branches  or  even  the  entire  tree. 

The  male  bark-lice  beneath  the  scales  on  the 
leaves  reach  maturity  the  same  season,  and  trans- 
form to  tiny  gnat-like  insects  (Fig.  4)  with  a 
pair  of  delicate  wings.  They  pair  with  the  partly 
grown  females  on  the  leaves,  and  die  at  the  ap- 
proach of  winter.  Before  the  fall  of  the  leaf  in 
autumn  the  young  females  collect  on  the  under 
side  of  the  smaller  branches,  where  they  spend 
the  winter  in  a  more  or  less  dormant  condition 
with  their  beaks  inserted  in  the  wood.  They 
complete  their  growth  in  spring  (Fig.  5),  and 
in  due  time  produce  the  so-called  "cotton,"  within 
which  the  eggs  are  imbedded. 


1907.]  THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS.  349 

THE  HATCHING  PERIOD. 

As  the  newly  hatched  young  are  especially  susceptible  to  the 
petroleum  insecticides,  which  act  by  contact,  a  definite  knowledge 
of  the  hatching  period  has  an  important  practical  value.  In  central 
Illinois  this  period  extends  approximately  from  June  15  to  July  20. 
In  and  about  Chicago  it  commonly  begins  about  two  weeks  later, 
and  continues  for  a  period  of  three  weeks,  this  retardation  being  ap- 
parently due  to  the  higher  latitude  and  to  the  neighborhood  of  Lake 
Michigan.  In  1905,  for  example,  Dr.  Folsom  found  that  the  young 
began  to  appear  in  Chicago  about  July  i,  and  were  all  out  by 
July  21  or  a  few  days  later,  but  that  thirty  miles  west  of  the 
city,  hatching  began  about  June  20.  Mr.  H.  E.  Weed  reports,  in 
Bull.  52  of  the  U.  S.  Bureau  of  Entomology,  that  in  1904  scarcely 
any  eggs  had  hatched  in  Chicago  by  June  25,  but  that  the  young  ap- 
peared rapidly  under  the  influence  of  a  few  days  of  warm  weather 
about  July  10.  The  recorded  dates  for  Colorado  approach  those 
given  for  Chicago.  In  Washington,  D.  C.,  according  to  Dr.  How- 
ard, hatching  of  the  eggs  begins  usually  in  late  May  or  early  Juner 
and  continues  into  July  and  sometimes  to  the  beginning  of  August. 

The  period  varies,  in  short,  as  to  its  beginning  time,  with  the 
advancement  of  the  season,  and  once  begun,  the  rapidity  of  the 
hatching  will  depend,  other  things  being  equal,  on  the  warmth  of 
the  weather.  It  is  also  influenced  locally  by  the  amount  of  foliage 
on  the  trees,  the  eggs  hatching  later  and  more  slowly  in  a  dense 
tree-top  than  in  one  more  open  to  the  sun. 

SUMMER  INSECTICIDE  MEASURES. 

Owing  to  the  manner  in  which  these  insects  obtain  their  food — 
that  is,  by  sucking  the  sap  through  a  tubular  beak — they  are  not 
susceptible  to  poisoning  by  way  of  their  food,  and  the  only  insecticides 
available  against  them  are  those  which  kill  by  contact,  and  of  these 
the  kerosene  mixtures  have  thus  far  been  found  the  most  useful. 
The  most  satisfactory  of  these  is  the  common  kerosene  emulsion, 
made  by  thoroughly  and  intimately  mixing  a  good  grade  of  kero- 
sene with  one  third  its  volume  of  a  strong  soap-suds,  and  diluting 
with  water  according  to  the  time  of  the  year  when  used.  Precise 
directions  for  preparing  and  applying  this  emulsion  may  be  found  in 
the  general  summary  at  the  end  of  this  paper. 

The  use  of  this  insecticide  for  the  maple  scale  dates  from  experi- 
ments made  by  me  in  1884,  intended  to  test  the  effect  of  kerosene 
emulsion  on  the  newly  hatched  young,  and  described  in  the  Four- 
teenth Report  of  the  Illinois  State  Entomologist.  They  showed 


350  BULLETIN  No.  112.  [January, 

that  practically  all  these  may  be  killed  by  dipping  the  infested 
leaves  in  dilute  emulsions  (those  used  varying  in  content  from  2.^/2 
to  10  per  cent,  of  kerosene),  unless  the  application  be  delayed  too 
long  after  hatching.  When  the  young  are  a  week  or  two  old  they 
are  partially  protected  by  a  waxy  covering  against  the  action  of  the 
oil.  The  test  of  death  used  was  a  thoroughly  reliable  one.  The 
young  were  at  this  time  so  small  and  transparent  that  the  action  of 
the  heart  could  be  readily  seen  under  a  microscope,  and  the  cessation 
of  this  action  was  the  mark  of  death  depended  upon.  As  the  maple 
scale  disappeared  from  my  neighborhood  in  1885,  no  further  experi- 
ments were  made  at  that  time. 

In  1904  the  Commissioners  of  the  North  Shore  Park  District, 
above  Chicago,  of  which  Robert  W.  Vasey  was  president,  engaged 
Mr.  H.  E.  Weed,  of  Chicago,  to  treat  one  hundred  and  twenty  soft 
maples  and  box-elder  trees  in  their  charge,  along  the  boulevards,  for 
the  destruction  of  the  cottony  maple  scale.  A  report  of  this  treat- 
ment by  Mr.  Weed  was  printed  in  Bull.  52  of  the  U.  S.  Bureau  of 
Entomology.  The  results  of  his  work  were  submitted  to  me  for 
examination  in  August  and  September,  1904,  by  Mr.  Vasey,  who 
sent  me  leaves  from  the  trees  which  had  been  treated  with  a  12  per 
cent,  emulsion. 

The  scale  insects  on  these  leaves  were  carefully  examined  at 
my  office  by  Mr.  Hart,  who  found  that  out  of  1781  scales  610  were 
alive  and  1171  were  dead.*  Practically  all  the  living  scales  were  on 
the  under  surface  of  the  leaves,  only  I  per  cent,  of  those  on  the  upper 
surface  being  still  alive.  The  ratio  of  the  dead  to  the  living  on  these 
leaves  was  60  per  cent. ;  but  as  it  seemed  likely  that  some  scales  were 
dead  before  the  spray  was  applied,  Mr.  Vasey  sent  me,  for  com- 
parison, at  my  request,  leaves  from  infested  trees  not  treated.  An 
examination  of  these  untreated  leaves  showed  that  22  per  cent,  of 
those  on  the  upper  surface  were  dead  and  4  per  cent,  of  those  on  the 
lower  surface.  Making  the  necessary  correction,  it  was  found  that 
57  per  cent,  of  the  scales  alive  when  the  trees  were  sprayed  had  been 
killed  by  the  treatment.  The  spray  thus  tested  was  applied  Au- 
gust 29. 

According  to  Mr.  Vasey,  the  insects  had  hatched  very  slowly 
that  year,  owing  to  the  backward  season,  but  had  been  in  condition 
for  treatment  with  the  kerosene  spray  for  some  three  or  four 
weeks  preceding.  It  will  be  seen,  consequently,  that  the  treatment 
was  too  late  to  produce  the  full  effect  upon  the  young.  Further 


*The  young  insects  were  by  this  time  so  opaque  that  the  movements  of  the  heart  could 
no  longer  be  seen;  but  it  was  found  that  living'  individuals,  when  displaced  and  inverted, 
made  slow  movements  of  the  leg's,  and  that  dead  individuals  were  not  only  motionless  but 
paler  and  often  discolored,  and  usually  more  or  less  dried  up. 


1907.}  THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS.  351 

work  showed  that  a  15  per  cent,  emulsion  was  injurious  to  the  tree, 
taking  nearly  all  the  leaves  from  the  box-elders  and  the  lindens,  and 
half  those  from  the  soft  maples.  In  this  same  year  (1904)  Mr.  S.  A. 
Johnson,  of  the  Col.  Agricultural  Experiment  Station,  made  a  num- 
ber of  laboratory  experiments  with  the  summer  treatment  of  this 
insect,  reaching  the  conclusion  that  after  the  young  are  a  week  or 
ten  days  old  they  are  not  easily  killed  by  the  kerosene  emulsion,  but 
that  before  reaching  this  age  they  may  be  effectively  treated  by 
sprays  of  as  low  a  strength  as  5  per  cent. 

The  following  year  (1905)  Dr.  J.  W.  Folsom,  of  the  University 
of  Illinois,  made  for  me  a  series  of  experiments,  opportunity  for 
which  was  provided  by  the  courtesy  of  Mr.  O.  C.  Simonds,  Super- 
intendent of  Graceland  Cemetery. 

A  10  per  cent,  emulsion  of  kerosene  was  applied  to  several  trees 
of  medium  size  with  the  use  of  a  Bordeaux  nozzle  on  an  extension- 
pole.  A  solid  stream  was  first  directed  against  the  egg-masses  in  order 
to  loosen  and  soak  them,  after  which  a  very  fine  spray  was  applied 
as  thoroughly  as  possible  to  both  sides  of  the  leaves.  A  solution  of 
whale-oil  soap  (one  pound  to  six  gallons  of  water)  was  applied  to 
an  eighth  tree  by  the  same  apparatus  and  with  the  same  care. 

The  effect  of  the  spray  was  tested  by  counting  both  dead  and 
living  scales  on  twenty-five  leaves  picked  at  random  from  different 
parts  of  each  tree,  one  series  of  counts  being  made  just  before  the 
spray  was  applied  and  another  as  soon  as  possible  after  it  had  dried 
away  and  taken  effect.  Among  the  trees  receiving  the  10  per  cent, 
emulsion  of  kerosene  were  one  tree  sprayed  July  3,  at  the  beginning 
of  the  hatching  period  of  the  scale,  one  treated  July  n,  at  about 
the  middle  of  this  period,  three  treated  July  19  and  20,  at  the  end 
of  the  period,  and  one  treated  twice,  once  at  the  middle  and  once  at 
the  end.  The  tree  receiving  the  soap  solution  was  sprayed  July  19 — 
that  is,  at  the  end  of  the  hatching  season. 

Four  hundred  and  eighty-four  thousand  scales,  borne  by  four 
hundred  and  fifty  leaves  from  these  various  trees,  were  critically 
examined,  and  classified  as  either  living  or  dead.  The  ratio  of  bene- 
fit— the  percentage,  that  is,  of  scales  actually  killed  by  the  spray — 
was  determined  in  all  cases  by  eliminating  from  the  calculation  the 
scales  dead  at  the  beginning  of  the  experiment,  and  figuring  the  per- 
centages only  on  the  number  of  scales  alive  when  the  spray  was  ap- 
plied. The  following  table  gives  the  essential  data  and  results  of 
these  experiments. 


352 


BULLETIN  No.  112.  [January, 

EFFECTS  OF  EXPERIMENTAL  SUMMER  SPRAY. 


Treatment 

No.  of 
trees 

Leaves 
ex- 
amined 

Scales 
ex- 
amined 

Percent, 
killed 
by  spray 

Insecticide 

Part  of 
hatching 
period 

/• 
10  per  cent.  Kerosene 

Beginning 

1 

75 

48,789 

33 

10  per  cent.  Kerosene 

Middle 

1 

50 

19,425 

64 

10  per  cent.  Kerosene. 

End 

3 

150 

281,271 

68 

10  per  cent.  Kerosene 

Middle 
and  end 

1 

100 

57,179 

82 

.1  Ib.  Whale-oil  Soap  to 
6  gal.  water 

End 

1 

75 

77,171 

43 

From  this  it  will  be  seen  that  75  leaves  bearing  49,000  scales 
were  examined  from  the  tree  sprayed  July  3,  and  that  only  33  per 
cent,  of  the  scales  on  this  tree  had  been  killed.  In  this  case  a  first 
inspection  was  made  ten  days  after  the  spray  was  applied,  and  a 
second,  seven  days  later.  The  trees  sprayed  once  July  n — at  the 
middle  of  the  hatching  period — and  from  which  50  leaves  bearing 
19,000  scales  were  examined,  showed  a  ratio  of  benefit  of  64  per  cent. ; 
that  is,  64  per  cent,  of  the  scales  alive  when  the  spray  was  applied, 
were  dead  a  few  hours  later.  In  other  words,  by  postponing  the 
treatment  from  the  3d  to  the  nth  of  the  month  the  effect  of  it  had 
been  nearly  doubled.  A  similar  but  somewhat  greater  effect  was 
produced  by  single  treatments  given  July  19  and  20,  when  the 
greater  part  of  the  eggs  were  already  hatched,  68  per  cent,  of  the  liv- 
ing scales  among  the  281,000  borne  by  the  150  leaves  examined  being 
thus  killed.  The  most  effective  treatment  was  a  double  spraying, 
one  application  at  the  middle  and  the  other  about  the  end  of  the 
hatching  period,  which,  as  shown  by  an  examination  of  57,000  scales 
from  100  leaves  of  the  tree  so  treated,  killed  82  per  cent,  of  the 
scales  alive  when  the  tree  was  sprayed.  That  is,  the  effect  of  the 
operation  had  been  increased  approximately  28  per  cent,  by  the  sec- 
ond spraying. 

A  comparison  of  the  scales  on  the  two  surfaces  of  the  leaves 
showed  that  the  ratio  of  those  killed  on  the  lower  surface  was  only 
72  per  cent,  that  cf  those  killed  on  the  upper  surface.  This  was  doubt- 


1907.]  THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS.  353 

less  due  in  part  to  the  fact  that  the  upper  surface  of  the  leaf  is  more 
exposed  to  the  spray  than  the  under,  and  possibly  also  in  part  to  the 
inferior  vitality  of  the  scales  on  the  more  exposed  surface  of  the 
leaf.  That  there  is  really  such  a  difference  is  shown  by  the  differ- 
ence in  ratios  of  dead  to  living  on  the  two  leaf  surfaces  before  the 
trees  were  sprayed.  The  general  average  of  all  the  counts  is  3.6 
per  cent,  of  dead  on  the  upper  surface  of  the  leaf  and  2  per  cent,  on 
the  lower. 

In  the  tree  sprayed  July  3  the  effect  on  the  scales  on  the  upper 
and  the  lower  parts  of  the  top  of  the  tree  was  brought  into  compar- 
ison by  examining  the  scales  on  25  leaves  from  each.  Twenty-two 
per  cent,  of  the  scales  on  the  upper  leaves  had  been  killed  and  35  per 
cent,  of  those  on  the  lower,  the  ratio  of  killed  being  more  than  half 
as  great  again  for  the  lower  leaves  as  for  the  upper.  This  is  doubt- 
less due,  at  least  in  part,  to  the  greater  and  more  prolonged  effect 
produced  on  the  lower  leaves  by  the  drip  from  the  upper  part  of  the 
top. 

We  may  infer  from  these  experiments  that  two  sprayings  with 
a  10  per  cent,  kerosene  emulsion,  one  applied  at  the  middle  and  the 
other  at  the  end  of  the  hatching  period,  separated,  that  is,  by  an  in- 
terval of  about  ten  days,  will  produce  the  maximum  effect  on  the  scale, 
and  that  they  may  be  expected  to  destroy  80  per  cent,  or  more  of  the 
insects  then  alive.  It  should  be  added  that  no  harm  to  the  tree  was 
done  by  any  of  these  treatments  except  a  slight  burning  at  the  edges 
of  the  leaves  of  the  tree  which  was  twice  sprayed.  This  appearance 
of  injury  was  perhaps  due  to  humid  weather  which  followed  the 
first  treatment,  delaying  the  evaporation  of  the  kerosene.  Two  trees 
were  treated  July  n  with  a  10  per  cent,  kerosene  emulsion,  at  a 
time  and  place  when  rain  was  falling  with  a  result  to  diminish  by 
half  the  killing  effect  of  the  spray. 

The  cost  of  the  10  per  cent,  emulsion  used  in  these  experiments 
was  4.3  cents  per  gallon,  and  the  trees  were  large  enough  to  require 
three  or  four  gallons  each  for  a  single  treatment. 

The  whale-oil  soap  solution  applied  at  the  end  of  the  hatching 
period  had  about  two  thirds  the  effect  of  the  corresponding  kerosene 
treatment,  as  shown  by  a  comparison  of  the  results  of  the  data 
already  given  for  the  latter  with  those  derived  from  an  examination 
of  77,000  scales  on  75  leaves  taken  from  the  tree  treated  with  the 
former  insecticide. 

WINTER  INSECTICIDE  MEASURES. 

Winter  spraying,  when  the  trees  are  bare,  has  the  advantage 
that  stronger  insecticides  may  be  used,  and  that  less  than  half  as 


354  BULLETIN  No.  112.  [January, 

much  liquid  is  needed  to  the  tree.  On  the  other  hand,  the  scales  are 
now  larger  and  firmer  and  more  resistant  to  the  insecticide  than  in 
summer. 

The  extensive  operations  against  this  scale  by  the  Superintend- 
ent of  Lincoln  Park  during  the  winter  of  1905-06  were  followed  by 
one  of  my  assistants,  Mr.  E.  O.  G.  Kelly,  sent  repeatedly  to  Chicago 
for  this  purpose.  Nearly  every  tree  and  shrub  in  this  park  infested 
by  the  maple  scale  was  sprayed  under  the  immediate  supervision  of 
Mr.  R.  W.  Braucher.  Two  thousand  six  hundred  and  seventy-three 
trees  and  4456  shrubs  were  sprayed,  nearly  half  the  trees  ranging 
from  large  to  very  large,  and  the  remainder  from  small  to  medium. 
The  materials  used  in  this  treatment  were  4153  gallons  of  kerosene 
and  3074  pounds  of  soap,  made  up  in  20,800  gallons  of  kerosene 
emulsion.  The  cost  of  the  latter  was  approximately  2  cents  a  gallon. 
With  the  outfit  used,  a  Fairbanks-Morse  power  sprayer  with  double 
"Vermorel"  nozzles,  it  required,  on  an  average,  five  minutes  to  spray 
each  tree,  or  an  hour  for  twelve  trees.  Eight  men  were  employed 
with  the  outfit,  making  an  average  service  of  forty  minutes  of  one 
man's  time  per  tree.  Six  and  seven  tenths  gallons  of  emulsion  were 
applied  to  the  average  tree,  at  a  total  cost  of  43  cents  for  both  ma- 
terials and  labor. 

In  spraying  operations,  ladders  and  long  canes  were  used  in  or- 
der that  all  parts  of  the  larger  trees  might  be  reached  by  the  spray. 
In  the  greater  part  of  the  work  19  and  20  per  cent,  emulsions  of 
kerosene  were  applied.  To  make  this  up  in  2OO-gallon  lots,  20  gal- 
lons of  water  and  27  to  30  pounds  of  "Tak-a-nap"  soap  were  placed 
in  the  mixing  tub,  and  steam  was  introduced  until  the  soap  was  dis- 
solved and  the  solution  was  boiling  hot.  Forty  gallons  of  kerosene 
were  then  slowly  pumped  into  the  tub,  and  the  mixture  was  pumped 
back  into  itself  until  the  kerosene  no  longer  rose  to  the  surface  when 
the  pumping  ceased.  The  emulsion  was  finally  diluted  by  adding 
hot  water  to  make  200  gallons. 

A  part  of  the  trees  examined  were  sprayed  between  December 
26  and  January  5,  and  others  January  u  and  13  and  March  30. 
The  effects  of  the  spray  were  determined  by  comparing  ratios  of 
dead  and  living  scales  on  trees  which  had  been  treated,  with  those 
from  others  examined  at  the  same  time  which  had  received  no 
treatment.  A  determination  of  the  condition  of  the  scales  subse- 
quent to  treatment  was  a  much  more  difficult  matter  at  this  season 
than  during  the  summer.  The  dormant  insects  themselves  were 
comparatively  large  and  dense,  and  changes  due  to  death  were  pro- 
duced but  slowly  in  the  cold  midwinter  weather.  From  twenty- 


1907.  J 


THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS. 


355 


seven  to  forty  days  actually  intervened  between  the  time  of  spraying 
and  the  time  when  the  test  inspections  were  made. 

It  will  be  sufficient  to  say,  without  entering  into  details,  that  a 
critical  examination  of  13,0x30  scales  taken  from  8  trees  showed  that 
86  per  cent,  of  them  had  been  killed  by  a  19  per  cent,  emulsion ;  and 
an  examination  of  23,000  scales  taken  from  1 1  trees  which  had  been 
treated  with  a  20  per  cent,  emulsion  showed  that  91  per  cent,  of  these 
had  been  killed.  Seven  trees,  two  of  which  had  been  sprayed  Janu- 
ary n  and  five  March  30  with  emulsions  containing  from  19  to  24 
per  cent,  of  kerosene,  were  examined  June  10,  49,000  scales  in  all 
being  counted,  with  the  result  to  show  that  in  this  case,  also,  91 
per  cent,  of  those  alive  when  the  treatment  was  applied  had  been 
killed  by  the  emulsion.  The  trees  covered  by  these  observations 
were  soft  maples,  lindens,  and  honey-locusts,  but  as  the  percentages 
of  benefit  do  not  differ  materially  for  these  different  species  they 
need  not  be  separately  given.  The  following  table  summarizes 
these  data. 


When  sprayed 


Per  cent. 

of 
kerosene 


Date  of 
count- 
ing 


Scales 
counted 


Percent, 
killed 


19 

20 

19-24 


Feb.  1 
Feb.  1-2 
June  10 


12,703 
23,061 
48,395 


86 
91 
91 


INJURY  TO  TREKS. 

As  one  of  the  results  of  an  examination  of  trees  previously 
sprayed,  made  by  my  inspector  June  1 1  to  13,  he  reported  so  serious  a 
damage  to  some  of  the  trees  as  to  cast  doubt  on  the  safety  of  the  kero- 
sene spray.  At  Graceland  Cemetery,  for  example,  some  soft  maples 
had  received  during  the  winter  an  experimental  treatment  with  a  25 
per  cent,  kerosene  emulsion,  evidently  prepared  in  the  usual  way,  and 
all  these  trees  were  in  a  conspicuously  poor  condition,  with  foliage 
thin,  pale,  and  shriveled,  while  that  of  unsprayed  trees  among  them 
was  heavy  and  dark  green.  Many  of  the  trees  in  Lincoln  Park  on 
which  an  emulsion  containing  19  or  20  per  cent,  of  kerosene  had 
been  used,  presented  the  appearance  of  a  similar,  although  less  seri- 
ous, injury.  A  few,  indeed,  were  dead,  and  dead  branches  were 
more  numerous  on  others  than  usual. 

After  a  study  of  the  report  of  my  own  inspector,  Mr.  E.  O.  G. 
Kelly,  on  the  condition  of  these  trees  last  June,  and  a  full  and  care- 
ful report  on  the  same  subject  made  to  Superintendent  Warder  by 
Mr.  R.  W.  Braucher,  in  charge  of  the  spraying  operation,  and  an 
examination  of  comparative  photographs,  made  under  Mr.  Brauch- 


356 


BULLETIN  No.  112. 


[January, 


er's  direction,  of  trees  of  various  species — some  of  which  had  been 
sprayed  and  others  of  which  had  not — it  seems  to  me  clear  that 
many  of  these  trees  were  already  in  a  more  or  less  enfeebled  state 
owing  to  the  light  and  sandy  soil  and  other  unfavorable  conditions 
affecting  their  growth,  that  many  treated  trees  had  been  further 
greatly  weakened  by  heavy  and  continuous  infestation  by  the  maple 
scale,  and  that  the  consequences  had  been  in  some  cases  intensi- 
fied by  the  action  of  the  kerosene.  This  is  especially  suggested  by 
the  fact  that  trees  seemingly  most  injured  but  not  actually  killed, 
presented  the  same  general  appearance — though  in  a  more  marked 
degree — as  many  of  those  which  had  not  been  sprayed  at  all.  Pre- 
cise and  extensive  experiments,  the  results  of  which  may  be  brought 
into  strict  comparison,  are  needed  to  show  the  strength  and  the 
amount  of  the  emulsion  which  it  is  safe  to  use  under  various  con- 
ditions and  on  various  kinds  of  trees. 

In  the  meantime,  in  view  of  the  fact  that  the  thorough  spraying 
of  the  top  of  a  tall  tree  in  winter  requires  a  large  amount  of  kero- 
sene emulsion,  much  of  which  must  fall  to  the  earth,  and  the  further 
well-known  fact  that  fruit-trees  may  be  severely  injured,  and  even 
killed,  by  kerosene  in  the  earth  about  their  roots,  it  will  be  prudent 
to  protect  the  ground  where  this  insecticide  is  used  by  some  imper- 
vious or  absorbent  covering,  such  as  a  sheet  of  canvas  or  a  layer  of 
straw,  the  latter  afterwards  to  be  removed.  Kerosene  will,  in  fact, 
remain  effective  in  the  ground  for  a  surprising  time,  and  this  fact 
is  the  basis  of  one  of  its  most  important  uses  as  a  subterranean  in- 
secticide.* Thousands  of  fruit-trees  have  been  destroyed  within  my 
own  knowledge,  by  its  careful  use  under  the  supervision  of  expert 
operators,  where  orchards  were  undergoing  treatment  for  the  San 
Jose  scale. 

Experiments  already  referred  to,  made  at  Denver,  Col.,  by  Mr. 
S.  A.  Johnson,  resulted  in  a  way  to  indicate  that  weaker  emulsions 
than  those  used  in  Chicago  may  be  depended  on  to  destroy  the  maple 
scale,  as  shown  by  the  following  table. 


Percentage  of  emulsion 

10 

12 

12K 

17 

20 

25 

33 

50 

November,  1903 
February,  1904 

88 
69 

94 

88 

99 

100 

98 

100 

100 
100 

*The  most  notable  instance  of  this  persistence  of  kerosene  in  the  earth  which  has  come 
to  my  knowledge  is  reported  to  me  by  Professor  T.  J.  Burrill,  of  the  University  of  Illinois, 
who,  in  company  with  Prof.  J.  C.  Blair,  of  the  Horticultural  Department,  once  lightly  sponged 
the  bark  of  a  pear-tree  with  pure  kerosene  as  an  experiment.  Nothing  unusual  was  noticed 
the  first  year,  but  the  second  year  the  tree  was  seen  to  be  unthrifty,  and  the  third  year  it  was 
dead.  When  dug  up  to  learn  the  cause  of  its  death,  the  odor  of  kerosene  was  still  distinct  and 
strong  in  the  earth  among  its  roots,  and  especially  in  the  bark  about  the  base  of  the  trunk. 
The  surplus  which  had  run  down  the  surface  of  the  bark  and  sunk  into  the  soil  had  remained 
all  this  time,  acting,  no  doubt,  continuously  upon  the  roots  and  on  the  bark  of  the  trunk  in  a 
way  to  kill  the  tree. 


1907.]  THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS.  357 

On  the  strength  of  these  experiments  Mr.  Johnson  recommends 
an  emulsion  one  sixth  of  which  is  kerosene.  Trees  treated  with  an 
emulsion  of  this  strength  in  the  winter  of  1904-05  were  nearly  free 
from,  scales  the  following  July,  and  in  January,  1906,  only  scatter- 
ing specimens  could  be  found.  In  view,  however,  of  the  difference 
in  climate  and  the  absence  of  data  as  to  parasitism,  these  results 
should  not  be  regarded  as  conclusive  for  Illinois. 

INSECT  ENEMIES. 

It  is  to  the  insect  enemies  of  the  scale  rather  than  to  any  human 
agency  that  the  escape  of  our  soft  maple  trees  from  complete  de- 
struction has  hitherto  been  due.  Probably  the  most  effective  enemy 


FIG.  6.     Coccophagus  lecami,  adult  chalcid  parasite  of  the  cottony  maple  scale. 
Length,  less  than  i\,  inch.    (J.  B.  Smith.) 

is  a  minute  black  four-winged  fly  (Coccophagus  lecanii,  Fig.  6) 
which  lays  its  eggs  in  the  bodies  of  the  young  scales.  The  resulting 
larva  lives  as  an  internal  parasite  of  the  insect,  develops  to  the  adult, 
and  emerges  through  a  rounded  hole  cut  in  the  back  of  the  scale.  Suc- 
cessive generations  follow,  and  the  scale  population  of  a  heavily  in- 
fested tree  may  be  almost  completely  destroyed  in  a  single  season 
by  the  parasite.  Scales  killed  by  it  may  be  readily  recognized  by 
the  hole  in  the  back,  and  by  their  smaller  size  as  compared  with 
living  individuals.  Several  other  related  species  are  known  to  infest 
this  scale  to  a  less  degree. 


358 


BULLETIN  No.  112. 


[January, 


A  conspicuous  and  very  efficient 
enemy  is  a  small  hemispherical  lady- 
bug  (Hyperaspis  binotata,  Fig.  7) 
about  an  eighth  of  an  inch  long,  jet- 
black,  with  a  small  dark-red  spot  on 
each  side  of  the  middle.  It  is  often 
seen  on  the  leaves  of  infested  trees 
and  on  plants  beneath.  The  white 
thick-bodied  larvae  of  this  species 
(Fig.  7,  rf),  which  feed  on  the  eggs 
of  the  scale,  may  often  be  found 
buried  in  the  egg-mass  or  crawling 
about  on  the  twigs.  The  pupa  of 
this  ladybug  is  formed  within  the 
cottony  egg-mass,  and  soon  changes  to  the  adult.  The  beetles  pass 
the  winter  wherever  they  may  find  shelter  about  the  tree  or  on  the 
ground  beneath.  The  larger  but  similarly-colored  "twice-stabbed 
ladybug"  (Chilocorus  bivulnerus,  Fig.  8),  with  its  black  spiny 
larva,  also  destroys  many  maple  scales. 


FIG.  7.  A  Ladybug-,  Hyperaspis  bino- 
'  tata.  enemy  of  cottony  maple  scale:  a, 
adult;  d,  larva;  6,  c,  antenna  and  palpus 
of  adult.  Adult  about  %  as  long-  as  Chi- 
locorus bivulnerus,  similarly  colored; 
larva,  white.  (Sanders,  U.S.  Department 
of  Agriculture.) 


FIG.  8.  A  Ladybug-,  Chilocorus  bivulnerus,  larva,  pupa,  and  adult,  enemy  of  cottony 
maple  scale.  Natural  size  indicated  at  rig-lit;  color  black,  adult  with  two  red  spots. 
(Comstock,  U.  S.  Department  of  Agriculture.) 

SUMMARY. 

1.  Injuries  by  the  cottony  maple  scale  are  commonly  periodical. 
A  period  of  destructive  abundance  and  following  scarcity  extends, 
on  an  average,  over  eight  or  ten  years,  the  disappearance  of  the  in- 
sect being  apparently  due  in  the  main  to  depredations  by  its  insect 
enemies. 

2.  A  partial  exception  to  the  foregoing  statement  is  presented  by 
the  existing  outbreak  in  northeastern  Illinois,  and  especially  in  Chi- 
cago, where  the  maple  scale  has  continued  injurious  for  at  least  six 
years,  and  gives  no  marked  present  evidence  of  a  general  decline  in 
numbers. 


PLATE  3.     Box -ELDER  TREES,  NOT  SPRAYED.     PHOTOGRAPHED  JUNE  23.     WEAK 

TREES    WITH    MANY    DEAD    BRANCHES. 


1907.]  THE  COTTONY  MAPLE  SCALE  IN  ILLINOIS.  359 

3.  The  area  injuriously  infested  by  this  insect  in  Illinois  last 
year    covers  parts  of  at  least  fifteen  counties,  distributed  throughout 
the  state  from  the  Wisconsin  line  to  Marion  county. 

4.  The  chief  food  plant  is  the  soft  maple,  but  linden  and  box- 
elder  are  almost  equally  liable  to  infestation.     The  elm  and  the 
honey-locust  are  the  principal  other  ornamental  trees  subject  to 
serious  injury. 

5.  There  is  but  one  generation  of  this  insect  each  year.  The  fe- 
males pass  the  winter  partly  grown  on  the  twigs  of  trees,  and  pro- 
duce eggs  in  late  May  or  in  June,  according  to  the  latitude  and  the 
weather  of  the  season.     These  eggs  hatch  in  June  and  July,  the 
young  insects  establishing  themselves  for  the  summer  on  the  leaves 
or  twigs,  from  which  they  suck  the  sap.     The  males  emerge  as 
winged  insects,  and  perish  at  the  approach  of  winter.    The  females 
at  that  time  collect  on  the  twigs  and  smaller  branches  for  hibernation. 

6.  The  most  useful  insecticide  is  kerosene  emulsion,  which,  if 
used  in  summer,  should  not  contain  more  than  10,  or  possibly  12^, 
per  cent,  of  kerosene,  and,  if  used  in  winter,  not  more  than  16  to  18 
per  cent.     As  a  summer  spray  this  emulsion  must  be  used  twice  in 
succession,  with  a  ten-day  interval  between  sprayings.     The  first 
application  must  be  made  when  about  half  the  eggs  are  hatched,  and 
the  second  at  about  the  end  of  the  hatching  period.    Two  treatments 
with  10  per  cent,  kerosene,  applied  to  badly  infested  trees  in  Chi- 
cago, the  first  July  n  and  the  second  July  20,  1905,  destroyed  82 
per  cent,  of  the  scales ;   a  single  treatment  July  1 1  destroyed  64  per 
cent. ;    and  one  July  19,  68  per  cent.     A  similar  treatment  July  3, 
on  the  other  hand,  killed  but  33  per  cent,  of  the  insects. 

7.  A  single  treatment  in  winter  with  a  19  or  20  per  cent,  emul- 
sion destroyed  more  scales  than  two  summer  treatments  with  a  10 
per  cent,  emulsion,  the  percentages  of  killed  varying  from  86  to 
91  per  cent. 

8.  Where  large  trees  weakened  by  unfavorable  conditions  or  by 
insect  attack  are  treated  with  strong  emulsions  in  winter,  they  are 
liable  to  injury  by  a  penetration  of  the  kerosene  to  the  roots.     Such 
trees  should  be -protected,  consequently,  by  covering  the  earth  be- 
neath the  trees  with  sheets  of  canvas  or  layers  of  straw,  or  some 
similar  absorbent  substance. 

9.  Kerosene  emulsion  is  made  as  follows :    Dissolve  one  pound 
of  common  soap,  or  half  a  pound  of  whale-oil  soap,  in  one  gallon  of 
water  by  boiling,  remove  from  the  fire,  and  add  two  gallons  of  kero- 
sene.    Then  with  a  spray  pump  force  the  mixture  back  into  itself 
for  about  five  minutes,  or  until  it  presents  the  appearance  of  a  thick 
cream  and  no  longer  separates  on  standing.     This  is  the  undiluted 


360  BULLETIN  No.  112.  [January, 

emulsion.  For  a.  mixture  containing  10  per  cent,  of  kerosene,  add 
seventeen  gallons  of  water  to  the  three  gallons  thus  prepared.  For 
an  1 8  per  cent,  kerosene  emulsion,  add  eight  gallons  of  water  to  the 
stock  solution.  Soft  water  is  to  be  preferred. 

10.  The  principal  insect  enemies  of  the  cottony  maple  scale  are 
minute  winged  parasites  which  lay  their  eggs  within  the  bodies  of 
the  female  parents ;  and  hemispherical  shining  black  ladybugs,  each 
with  two  red  spots  on  the  back,  the  larvse  of  which  devour  the  eggs 
in  spring  within  the  cottony  masses  beneath  the  female  body. 


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